This application relates to variable optical attenuators, and more particularly, to variable optical attenuators for use in various optical devices and systems, including optical communication networks.
A variable optical attenuator (VOA) is a device designed to attenuate an intensity or power level of an input optical beam in a controlled manner to produce an output optical beam with different attenuated intensities. Such a device is desirable in various applications including optical fiber devices and optical communication networks.
For example, it may be desirable to place a VOA in front of an optical receiver to limit the received optical power of an incoming optical signal to a certain range to avoid saturation of the optical receiver while still maintaining the signal-to-noise ratio at an acceptable level. In another example, a VOA may be placed to regulate the optical output of a laser diode transmitter without changing its driving current so that the current-dependent laser wavelength and line width are not changed by such power regulation. In a further example, a VOA may be placed between two Erbium Doped Fiber Amplifiers (EDFA) to compensate for the gain tilt caused by the variation in the pumping power. In yet another example, VOAs may be used with a demultiplexer to individually adjust the power levels of different optical channels to form a dynamic gain equalizer for applications such as maintaining signal quality at all optical channels in entire optical networks, especially in long haul networks where multiple stages of optical amplifiers are installed. Furthermore, VOAs may be used in connection with optical add/drop multiplexer (OADM) and optical cross-connect (OXC) switch sites to compensate for the power variation caused by a change in the optical channel number.
Therefore, there is a need for single-channel and multi-channel VOAs, and especially a need for VOAs with integrated packages having power monitoring and servo control adapted for a variety of applications.